“If it were anyone but you, Craig,” I replied frankly, “I’d be tempted to call him something.  But you—­well, what’s the answer?  How do you know?”

“I wonder if you have ever heard of the Reichert blood test?  Well, the Carnegie Institution has recently published an account of it.  Professor Edward Reichert of the University of Pennsylvania has discovered that the blood crystals of all animals and men show characteristic differences.

“It has even been suggested that before the studies are over photographs of blood corpuscles may be used to identify criminals, almost like fingerprints.  There is much that can be discovered already by the use of these hemoglobin clues.  That hemoglobin, or red colouring matter of the blood, forms crystals has been known for a long time.  These crystals vary in different animals, as they are studied under the polarizing microscope, both in form and molecular structure.  That is of immense importance for the scientific criminologist.

“A man’s blood is not like the blood of any other living creature, either fish, flesh, or fowl.  Further, it is said that the blood of a woman or a man and of different individuals shows differences that will reveal themselves under certain tests.  You can take blood from any number of animals and the scientists to-day can tell that it is not human blood, but the blood, say, of an animal.

“The scientists now can go further.  They even hope soon to be able to tell the difference between individuals so closely that they can trace parentage by these tests.  Already they can actually distinguish among the races of men, whether a certain sample of blood, by its crystals, is from a Chinaman, a Caucasian, or a negro.  Each gives its own characteristic crystal.  The Caucasian shows that he is more closely related to one group of primates; the negro to another.  It is scientific proof of evolution.

“It is all the more wonderful, Walter, when you consider that these crystals are only 1-2250th of an inch in length and 1-9000th of an inch in width.”

“How do you study them?” I asked.

“The method I employed was to take a little of the blood and add some oxalate of ammonium to it, then shake it up thoroughly with ether to free the hemoglobin from the corpuscles.  I then separated the ether carefully from the rest of the blood mixture and put a few drops of it on a slide, covered them with a cover slip and sealed the edges with balsam.  Gradually the crystals appear and they can be studied and photographed in the usual way—­not only the shapes of the crystals, but also the relation that their angles bear to each other.  So it is impossible to mistake the blood of one animal for another or of one race, like the white race, for that of another, like the black.  In fact the physical characteristics by which some physicians profess to detect the presence of negro blood are held by other authorities to be valueless.  But not so with this test.”